An anode of a lithium ion (Li-ion) battery having high power as presently commercialized is mostly made of graphite. However, the theoretic electric capacity is only up to about 372 mAh/g. In order to overcome the limitation resulting from the insufficiency of the electric capacity, studies to find a novel anode are widely developing. However, no matter which of a tin-based or a silicon-based material is used for an anode, the fact that the dramatic volume expansion and shrinkage caused by lithium ion insertion and extraction during charging and discharging of the battery becomes the biggest hindrance to successfully commercialize the alloyed materials used for an anode at present. The main reason why silicon-based material is given the most effort to develop as a material for an anode applicable to a Li-ion battery versus other suitable materials is its abundance in the earth's crust and its intrinsically high theoretical capacity (4200 mAh/g). However, the anode tends to deteriorate and break so that the structure of the anode is easily fractured and pulverized. After several cycles of charging and discharging the battery, the electric capacity of the battery is rapidly decreased to an almost fully consumed extent. Therefore, these disadvantages restrict the material's possible commercial applications.
In order to overcome the problem caused by the high variation in volume, a method commonly used in the technical field is to coat a silicon powder with a conductive carbon. This method can efficiently reduce the shrinkage ratio in volume of the silicon powder and improve the problem of poor conductivity of silicon as well. It would be the most beneficial way for the purpose of cost reduction. Graphene is a mono layer of graphite with a perfect sp2 configuration and a two-dimensional flat plane structure. Recent progress in research shows that graphene exhibits a lot of particular properties such as high mechanical strength, high specific surface area, high electron conductivity and good chemical stability, so that it has been used in several energy technology applications. In the prior art, silicon and graphene were combined in order to prepare a silicon/graphene composite which was applied to the anode of the Li-ion battery. The graphene contained in the composite acts as a buffer layer, improves the poor conductivity of silicon, and improves the stability of the cycle performance of the battery during charging and discharging.
Although the stability of charging and discharging the battery can be improved when silicon powder appears in a form of the composite, the problem presently encountered is that the silicon powder is still unable to be uniformly dispersed on the layers of graphene. This unavoidably causes the deterioration of the electric capacity that accompanies the cycles of charging and discharging the battery.
The addition of some appropriate additives or the use of a chemical functionalization method can be used to improve the poor dispersion of silicon on the graphene layers. However, these methods significantly increase the cost of the material synthesis significantly. Therefore, there is an urgent need to provide a simple, low-cost method to improve the dispersion of silicon powder.